Numerous systems and processes for polymerizing olefins are known. Introduction of various compounds into polymerization reactors to control polymer product properties is also known. For example, U.S. Pat. No. 6,022,933 to Wright, et al., discloses the addition of a “catalyst poison”, such as oxygen, to a fluidized bed reactor used to produce high density polyethylene using bis-triarylsilyl chromate catalyst systems. The catalyst poison is added directly to the reactor or in a gas recycle line at a location downstream of the associated recycle gas cooler. The '933 patent discloses that the catalyst poison is to be introduced into the reactor in the range of about 0.005 to about 0.5 part by volume per million parts by volume of ethylene feed to the reactor. The catalyst poison is added in this manner to increase environmental stress crack resistance of articles made with the polymer produced. The '933 patent refers to the addition of oxygen as “oxygen addback”. Another effect attributed to the “oxygen addback” is lowering the molecular weight of the high density polyethylene produced.
U.S. Pat. No. 4,803,251 to Goode, et al., discloses a process for the reduction of sheeting during polymerization of alpha-olefins by the introduction of positive charge generating additives or negative charge generating additives into the polymerization reactor to neutralize the static charge in the reactor. The polymerization processes disclosed are for use with titanium or vanadium catalysts with aluminum cocatalysts. Positive charge generating additives are identified as alcohols containing up to 7 carbon atoms, oxygen, and nitric acid. Methanol is described as the preferred positive charge-generating additive. Negative charge generating additives are identified as ketones containing up to 7 carbon atoms such as acetone and methyl isobutyl ketone. The '251 patent describes that the additives are to be added to the reactor. Introduction of the additives to the recycle stream “just upstream of the inlet to the bottom of the reactor vessel” is described and exemplified. This location is downstream of the recycle stream compressor and cooler.
Addition of compounds to the recycle gas stream in olefin polymerization systems is known. For example, Published U.S. Patent Application 2004/0236040 to Mihan, et al., discloses the introduction of a liquid catalyst poison upstream of a cyclone separator positioned in the recycle stream. The liquid catalyst poison serves to “wet” fine dust particles to facilitate removal of the particles from the recycle gas in the cyclone. Another effect attributed to the catalyst poison wetting the dust particles is that the catalyst poison is removed from the circulating gas to prevent it from reaching the reactor where it “can have an adverse effect on the polymerization reaction.” The Application also indicates that the fine dust wetted by the catalyst poison that is not removed in the cyclone serves to avoid undesirable polymerization and deposit formation in the circulating gas. The Application discloses that the catalyst poison must have a boiling point above the maximum temperature within the recycle stream.
U.S. Pat. No. 5,066,736 to Dumain, et al., discloses the addition of an activity retarder into a reaction system for polymerization of alpha-olefins, particularly linear low density polyethylene. The activity retarder may be a polymerization inhibitor. The retarder is added to the polymerization system to control the temperature within the polymerization reactor. The retarder may be added directly to the reactor; to a monomer feed line; to a recycle separator device such a cyclone separator, to a recycle line from the cyclone separator, or to a reaction mixture recycle line located downstream of a heat exchanger used to cool the reaction mixture recycle stream.